An automobile passing through the shower bath at the first conveyor belt car wash in Chicago in 1925. Note how the top is thoroughly washed by the man on the second level runway.
Workers at the car wash hose-down the body and use soap and a brush to clean the body. The running gear (the undercarriage) of the cars are cleaned by water pipes underneath the car.
At the end of the cleaning process the cars are hand dried with towels as they proceed through the laundry.
The result is a spic and span automobile.